Method of making foil wound electrical coils



Feb. 23, 1965 w. F. M. GRAY ETAL METHOD OF MAKING FOIL WOUND ELECTRICAL COILS 2 Sheets-Sheet 1 Original Filed March 15. 1957 Feb. 23, 1965 w. F. M. GRAY ETAL 3,170,225

METHOD OF MAKING FOIL WOUND ELECTRICAL COILS Original Filed March 15, 1957 2 Sheets-Sheet 2 JIM/275w. W/l/ rdFM. 61;; E6726 0. M056];

United States Patent F 3,170,225 METHOD OF MAKING FOIL WOUND ELECTRICAL COILS Willard F. M. Gray, Hancock, and Rene 0. Moser, Pittsfield, Mass., assignors to General Electric Company, a corporation of New York Original application Mar. 15, 1957, Ser. No. 646,313, new Patent No. 2,977,556, dated Mar. 28, 1961. Divided and this application June 8, 1960, Ser. No. 34,691

5 Claims. (Cl. 29-15557) This application is a division of co-pending application Serial No. 646,313, filed March 15, 1957, now Patent 2,977,556, issued March 28, 1961.

The present invention relates to electrical coils or windings, and more particularly concerns foil-wound induction coils and a method of making them, wherein the coils incorporate ducts for circulation of cooling media and are adapted especially for comparatively large transformers and other electrical induction apparatus.

By the term foil-wound induction coil is meant a coil of given axial length formed by fiatwise winding on itself a suitably insulated ribbon or strip of low specific electrical resistance material whose width is substantially equal to the axial length of the coil and whose thickness corresponds to that of the foil form of thematerial, i.e., no more than a few mils, so that each turn of the ribbon or strip constitutes one complete layer of the coil.

The use of foil windings for transformeres, especially large commercial frequency power transformers, offers several advantages. A substantial reduction in the space occupied by the coils is afforded, and the magnetic core can also be made smaller, without sacrifice of the electrical capacity of the transformer. Furthermore, the foil configuration of the coil material facilitates winding and tap insertingprocedures and lends itself more readily to mechanization of these operations as compared to the more conventional wire coil arrangements for transformers.

Further advantages are greater mechanical strength to resist internal electromagnetic forces resulting from short circuit currents, particularly short circuits between taps, and much more uniform inherent distribution of transient voltage stresses, such as lightning surges, throughout the winding as compared with conventional wire wound coils.

In continuously winding the primary and secondary coils of a foil-wound transformer, it is important that the turns of foil and insulation on the coil be smooth and wrinkle-free, in order to avoid irregularities in the coil winding which are susceptible to electrical breakdown during operation and which'result in irregularly formed coils taking up excessive space. Diificulty in this regard is especially experienced in attempts to wind sheet material of large widths, such as 60 inches or more, in order to formlarge size foil-wound coils for power transformers and other high-rating induction apparatus. sheets are particularly subject to wrinkling and other surface irregularities both in being handled before the winding procedure and in the course of winding. To overcome this difiiculty, it has been found desirable to arrange a roller member in pressure contact with the sheets as they are laid on the coil winding.

However, due, to the necessary provision of circumferentially spaced generally axially extending ducts at intervals through the radial build of the'wound foil structure for the circulation of cooling and insulating fluid,

the surface of the coil as it is being wound does not present a sufficiently smooth continuous base on which the pressure roller may ride, and ,as a result the foil and associated insulating sheets may bedeformed, the wind ing will not have the desired smoothness and uniformity, and the winding apparatus will nndergo a severe bumping Such large 3,170,225 Patented Feb. 23, 1965 efiect which subjects it to undue wear and may cause damage to the sheets being wound.

Apart from the difficulties presented in attempting to wind large foil-wound induction coils as mentioned, it 7 has not previously been considered feasible for other reasons to make large size transformers using foil conductors. Heretofore, it was thought that if the axial length of foil-wound coils was extended to large commercial frequency power transformer sizes, i.e., of the order of a-mans height or greater, the current in the correspondingly wide low resistance foil material would not distribute itself evenly throughout the cross sections of the strip, thus causing uneconomical use of the conductor material and excessive temperature differentials or local heating. It was further thought that eddy currents induced in the wide induction strip by leakage flux effects would accentuate these conditions.

Unexpectedly, however, actual tests of foil-wound coils of such sizes on conventional magnetic cores have shown that such adverse effects are not produced to any substantial extent and that temperature gradients throughout the coil are surprisingly low and uniform, both axially and radially.

It is an object of the present invention to provide improved induction coils formed of sheet material, especially foil-wound transformer coils, and a method of making the same.

It is another object of the invention to provide foilwound electrical coils, especially for transformers of large size, wherein the foil-wound coil incorporates ducts for circulation of cooling and insulating media and wherein the layers of foil and associated insulation are smooth, wrinkle-free and tightly wound.

It is a further object of the inventionto provide foilwound coils incorporating duct-forming spacer members wherein a smooth, continuous base is provided for supporting pressure means used in forming the foil-wound coils, and to avoid intermittent jolting of the pressure means as it rides on the coil being wound.

It is still another object of the invention to provide a method of making foil-wound coils of the above type wherein the duct-forming spacers are placed and maintained in properly spaced positions during the winding process.

There is provided in accordance with the invention a foil-wound coil for electrical induction apparatus comprising concentric layers of insulated foil which is at least inches wide, and as much as -90 inches in width, and including means between adjacent layers of the coil for forming ducts extending throughthe coil to provide for circulation of cooling media, the foil-wound coil being characterized by; extremely tight, smooth, wrinkle-free layers and havinghigh mechanical strength for resisting stresses such as may be produced by short circuit conditions in a high voltage transformer.

, To produce a foil-wound'coil of the above type, the

invention provides a method of making a foil-wound c011 incorporating cooling ducts which comprises windviding support in the coil for continuously sustaining the pressure being exerted on thesheet material.

In one of its embodiments the present method comprises winding a coil of insulated foil material, introducing during the winding process between the turns of the coil .a plurality of juxtaposed-permanent and auxiliary elongated members extending along the coil, and

thereafter removing the auxiliary elongated members from the'foil-wound element after it has been formed,

'following description taken in conjunction .thereon.

thus leaving spaced cooling ducts extending through the foil-wound element. There is thereby provided by the above-described plurality of auxiliary and permanent members a firm continuous support on which the pressure means, forcing the sheet material against the coil, may ride smoothly.

The invention will be better understood from the with the accompanying drawings in which:

FIG. 1 is a perspective view of apparatus for winding coils of sheet material in accordance with the present invention; 7

FIG. 2 illustrates one embodiment of the present wind ing method;

FIG. 3 illustrates another embodiment of the present winding method;

FIG. 4 is a fragmentary view in cross-section of a foil-Wound coil element which may be "formed in accordance with the present invention; and

FIG. 5 shows a variation in the arrangement of spacer bars which may be used in practicing the invention.

Referring now to the drawings, and particularly to FIG. 1, there is shown a typical arrangement for winding a coil-wound transformer coil in accordance with the invention, wherein a sheet of metal foil 1, such as aluminum, from supplyroll 1a is simultaneously wound with a sheet of insulation 2, such as kraft paper, from supply roll 2a concentrically around a suitable support, preferably 'an insulating cylinder 4 (see FIGS. 2 and 3),

mounted for rotation on mandrel 3. As shown, the insulating sheet 2 is generally wider than the metal foil sheet 1 so that the insulation layers interposed between adjacent foil turns extend substantially beyond the foil edges and thereby prevent arching between the edges of different foil turns during the operation of the coil in a transformer.

The relative dimensions of the parts shown in the drawings are exaggerated for the purposes of clarity and are not intended to represent the actual scale of the components as used in practice. For large induction apparatus, such as power transformers to which the present invention is particularly applicable, the foil and insulation sheets 1, 2 would by way of example approximate 60 inches in width but may range from '50-'90 inches in width. With such wide sheets, it has been found necessary to provide means such as roller 5 in pressure contact with the sheets as they are laid on the coil to keep them in a completely smooth and flat condition and to iron out any wrinkles which might be present In order, further, to provide the necessary tightness of the layers as they are wound so as to produce a finished'coil having the' least radial dimension, considerable tension (e.g., of the order of 6000 lbs./ sq. inch) is placed on the foil being wound.

The thickness of the foil sheet 1 may vary from about A -mil to about 30 mils, the thinner foil being normally used for the high voltage coils and the thicker foil for the low voltage'coils. The insulation (paper) sheet may 4) preferably includes elongated spacers 6 arranged at intervals in the coil Winding and suitably spaced to define channels 6 of desired size. arranged axially at intervals in. the winding, contact roller 5 during thewinding process would undergo a bumping action by intermittently striking the spacer bars 6 as it rides with substantial pressure against the periphery of the coil. The winding turns Iwould, as a consequence, become deformed and there would be considerable risk of damage both to the insulationlayers and foil layers which could ultimatelyv lead to prema- If spacers 6 are merely sequence.

4 ture breakdown of the coil under operating conditions.

There would, furthermore, be an undesirable vibration transmitted to the winding apparatus leading to its improper operation and early failure.

To obviate these difficulties, there is provided in accordance with one embodiment of the invention a plurality of removable auxiliary strips 7 arranged in and substantially filling the duct spaces defined by the permanent spacer bars 6, as shown in FIG. l, so as to provide a substantially smooth, continuous base on which the pressure roller 5 may ride during the winding process. Preferably, the radial dimension of auxiliary strips '7 is slightly smaller than that of the permanent spacers 6 in order to facilitate theirremoval from the completely wound structure. If desired, the auxiliary strips 7 may be waxed or otherwise suitably lubricated for this purpose. They are also preferably made of sufiicent length to project from the edge of the coil, so that they can be more easily grasped for removal after completion of the winding. Both the permanent spacers 6 and auxiliary strips 7 may be of any desired material, either of insulating or metallic composition, and may, for example, consist of pressboard, wood, aluminum or other material.

The duct-forming spacers 6 and the auxiliary filler strips 7 can be introduced in various ways into the coil during the winding procedure. FIG. 2 illustrates one method of inserting these members which may be carried out manually. In this process, the starting ends of the foil and insulation strips 1, 2 are securely attached by any suitable means to the surface of insulating cylinder 4,

and as the winding of these strips around cylinder 4 proceeds, the operator inserts at the nip between the insulating sheet 2 and the underlying surface the permanent spacers 6 and auxiliary members 7 alternately in Auxiliary strips 7a as shown in FIG. 2 is just being inserted into place adjacent a previously .positioned spacer bar at the Winding stage illustrated. Usually, the permanent spacers 6 as well as the auxiliary members 7 are held suflioiently secure in the'winding by the pressure of the overlying foil and insulating sheets, but if desired the permanent spacers 6 may be'coated with a suitable adhesive to ensure their secure attachment to the winding turn on which they are placed, or in the winding stage shown in FIG. 2, on the cylinder 4.

In a usual construction in accordance with, the invention, only one complete annular row of spacer'ducts will be provided in the winding at a time, so that in the pro- .cedure illustrated in FIG. 2 permanent spacers 6 and auxiliary members 7 will be inserted only until the initial bar 6a of that series is reached after one revolution of mandrel 3. Thereafter, a number of turns of the foil and interposed insulating sheets will be wound on the coil before another series of spacer bars and filler strips is provided, as indicated in FIG. 4.

FIG. 3 shows a different method of inserting the spacer bars and filler strips. In this process, the permanent and auxiliary members 6,7 are mounted on a carrier web 8 of. paper or the like, bars 6 preferably being secured to the surface of the web by adhesive or other suitable.

- means, while auxiliary strips 7 are merely laid freely in the spaces therebetween. The end of the web 8 is then inserted in any desired manner into the starting nip at the beginning of the wind and is continuously fed into the winding as cylinder 4 rotates. As will be understood, the length of the web will be'equivalent to the circumference of the cylinder 4 (or the periphery of the underlying coilsurface in subsequent duct formations)yto pro vide the desired complete circumferential row of ducts.

In both procedures described, after the winding of the coil is completed, the projecting auxiliary filler strips .7

are merely grasped at their ends and slid lengthwise.

out or the foil-wound structure,'leaving a series of regu- I auxiliary strips extending inwardly from opposite sides of the coil. Even if a gap should be left inside the coilbetween the inner ends of two such short filler strips, sufiicient support for the contact roller 5 will be provided by the spaced strips to prevent it from jolting.

Although not shown, conducting taps of desired type may be attached to the foil in any suitable manner at dilferent stages of the winding procedure.

It will be understood that in any duct series wherein the ducts extend substantially axially as shown in FIGS. 2, and 3 the width of the spacer bars 6, the intervals at which they are spaced, and the width of the auxiliary strips 7 should be proportioned to substantially fill the entire space in the row involved. Since the periphery of the coil becomes larger as the winding progresses, it may be desirable to suitably modify the width of the bars, ducts and filler strips for the subsequent duct rows to ensure a continuous, firm, smooth supporting surface on which the pressure roller 5 may ride.

In a typical foil-wound coil the spacer bars 6 will have a radial dimension of about Ar-V2 inch, and the spacing between adjacent bars will vary from M4 inch to 3 inches depending usually on the distance of the spacer row from the center of the coil.

The arrangement of the spacer bars 6 in the coil may differ from that shown in FIG. 4. In certain cases, for example, it is desirable to arrange the spacer bars in definite radial alignment rather than as shown, such radial alignment having been found to provide the coil with improved resistance to radial stresses which may be produced in the coil by short circuit conditions.

FIG. 5 shows a different embodiment of the invention, wherein the permanent spacers 6b and the removable auxiliary strips 7b are arranged in the winding at an angle to the axis of the coil. With this arrangement, it will be evident that the angled spacers 6b themselves provide a continuous support for the pressure contact roller 5 described above, since the axis of the latter is normally parallel to the axis of the coil and the roller thus will always be supported by a plurality of spacer bars 6b. Since in this case strips 7b need not fill the entire depth of the duct space to provide an adequate support for the pressure roller, these auxiliary strips may be of lesser height than the adjoining spacer bars 6b to facilitate their removal from the wound coil. In this embodiment the strips 7b serve principally as spacer elements to properly align and maintain the permanent bars 6b in position during the winding process.

The foil-wound coils produced in accordance with the invention are characterized by wound turns of both the foil and insulation sheets which are entirely free of wrinkles, creases or other irregularities, which otherwise would contribute to poor electrical properties of the coil' and lead to premature breakdown of the transformer. Moreover, the foil-Wound coils of the present invention are very tightly wound and extremely compact, and are characterized by an overbuild of about 1%. Overbuild as used herein is intended to mean the percent difference between the actual radial dimension of the wound coil and the sum of the radial dimensions of the superposed coil components. As will be evident, the tighter the coil is wound the lower will be its overbuild. Because of its tight and compact nature the present coil offers particularly good mechanical resistance to axial and radial stresses produced ,by short circuit conditions, and also has improved heat transfer 1 properties.

There are thus provided by the invention foil-wound coils which are particularly suitable for use in high volt- 6 age transformers, and an economical and practical method of winding such coils while incorporating cooling ducts therein without deforming or otherwise damaging the coil components.

While the present invention has been described with reference to particular embodiments thereof, it will be understood thatnumerous modifications may be made by those skilled in the art without actually departing from the scope of the invention. Therefore, the appended claims are intended to cover all such equivalent variations as some within the true spirit and scope of the invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. The method of making a wound coil of insulated foil for electrical induction apparatus wherein the coil incorporates means for passage of cooling media therethrough which comprises winding the insulated foil material into a coil while providing pressure means resting on the insulated foil material forcing the same toward the underlying coil surface as it is being wound so as to form tight, wrinkle-free layers thereof of the coil, and introducing during said winding a plurality of elongated members extending at an angle to the axis of said coil between certain layers of said coil for defining ducts extending through said coil, the elongated members being angled sufficiently so that the pressure means rests simultaneously on portions of adjacent elongated members, thereby providing a substantially smooth supporting base in said coil for continuously sustaining said pressure.

2. The method of making a coil of insulated foil for electrical induction apparatus, said coil incorporating ducts for circulation of cooling media, which comprises Winding the insulated foil material into a coil while providing pressure means resting on and pressing the insulated foil material toward the underlying coil surface, providing between adjacent turns of said coil during the winding thereof a plurality of juxtaposed elongated members extendingalong said coil for providing a substantially viding between adjacent turns of said coil during the winding thereof a plurality of juxtaposed elongated members extending at an angle to the axis of said coil, the elongated members being angled sufiiciently so that the pressure means rests simultaneously on portions of adjacent elongated members, whereby a substantially smooth support base is provided for continuously sustaining the Pressure thereon, certain ones of said elongated members being smaller in height than the remaining elongated members, and thereafterremoving said certain ones of said elongated members from between said remaining elongated members in the wound coil thereby leaving ducts extending through said coil! 4. The method of making a foil wound element for electrical induction apparatus which comprises winding on a cylindrical support a sheet of metal foil and a sheet of insulating material wider than said metal foil so as to provide a coil of concentrically wound alternating layers of foil and insulating material with the insulating material projecting axially beyond the foil, said sheets being urged by pressure contact means toward the cylindrical support as they are wound thereon, interposing between adjacent turns'of said coil during the windingthereof a plurallty ofjuxtaposcd elongated members so that said members form a complete circumferential ,layer between said turns for providing a substantially smooth support base in said coil for continuously sustaining the pressure thereon, and

thereafter removing alternate ones of said elongated members so as to leave ducts extending through said Wound coil between the remaining elongated members.

5. The method of making a foil Wound element for electrical induction apparatus which comprises winding on a cylindrical support a sheet of metal foil and a sheet of insulating material so as to provide a coil of concentrically wound alternating layers of foil and insulating material, said sheets being urged by pressure contact means toward the cylindrical support as they are Wound thereon, inserting between adjacent turns of said coil a sheet member having mounted thereon a plurality of juxtaposed elongated members for providing a substantially smooth support base in said coil for continuously sustaining the pressure thereon, said plurality of juxtaposed elongated members forming a complete circumferential layer between said turns, and thereafter removing alternate ones of said elongated members so as to leave ducts extending through said wound coil between the remaining elongated 'members.

7 References Cited by the Examiner UNITED STATES PATENTS 1,636,266 7/27- Wilkenson 336-185 1,641,272 9/27 Horelick 336-185 X 2,276,980 3/42 Jacobi 242- -56.1 2,422,037 6/47 Paluev 336185 2,510,786 6/50 Weiss 242--56.1 2,521,513 9/50 Gray 336-223 2,505,592 4/51 Pearce 336223 2,700,207 1/55 Zimsky 29l55.57 2,850,707 9/58 Wroblewski et al. 336- 207 2,863,130 12/58 Gray et al 336207 2,998,583 8/61 Worcester 336223 WHITMOREA. WILTZ, Primary Examiner.

20 IOHNF. CAMPBELL, Examiner. 

2. THE METHOD OF MAKING A COIL OF INSULATED FOIL FOR ELECTRICAL INDUCTION APPARATUS, SAID COIL INCORPORATING DUCTS FOR CIRCULATION OF COOLING MEDIA, WHICH COMPRISES WINDING THE INSULATED FOIL MATERIAL INTO A COIL WHILE PROVIDING PRESSURE MEANS RESTING ON AND PRESSING THE INSULATED FOIL MATERIAL TOWARD THE UNDERLYING COIL SURFACE, PROVIDING BETWEEN ADJACENT TURNS OF SAID COIL DURING THE WINDING THEREOF A PLURALITY OF JUXTAPOSED ELONGATED MEMBERS 